Photosensor arrays are commonly used in electronic cameras, including both still and video cameras. These photosensor arrays are often incorporated as components of image sensor integrated circuits along with circuitry for reading images from the photosensor array. Typically, these devices are integrated circuit die having a rectangular array of pixel sensors, where each pixel sensor includes at least one photodiode or phototransistor adapted for detecting light, together with circuitry for sensing the sensors to generate an electronic signal representing light detected by the sensors, and for exporting that signal to off-chip circuitry. Most such photosensors are of the topside-illumination type, designed to receive light into the pixel sensors through the same die surface into which controlling transistors, including transistors of the sensing and signal exporting circuitry, are built.
While photosensor arrays may be of the “black and white” type, often used for security cameras, in 2012 most video and still camera applications demand color.
A common type of color photosensor array has color filters deposited over topside-illuminated pixel sensors. These filters are often in a four-pixel, three-color, pattern that is repeated, or tiled, throughout the array; the filters in such arrays are typically colored such that-one filter admits red light to a first sensor, another admits green light to a second sensor, another admits blue light to a third pixel sensor, and the fourth filter of each pattern admits one of red, green, or blue light to a fourth pixel sensor.
In many camera systems, outputs of the pixel sensors from the patterns are processed to provide traditional red, green, and blue (RGB) color signals, such as may be used in an additive color display system to provide a full-color image. Red-Green-Blue has become the standard for color electronic cameras and color computer monitor video.
In recent times, backside-illuminated (BSI) photosensor arrays have been developed. These photosensor arrays typically are built on thinned die, with controlling transistors on a first surface of the die, but designed to receive light through a second, or backside, surface of the die opposite the first surface.
While some BSI photosensors use a pattern of filters printed onto the backside surface to selectively admit red, green, or blue light to sensors of each tiled pattern, it has been found that pixel sensors can be designed to have color response determined by junction profiles and depths in the sensors. In FIG. 1 of US published patent application PCT/US01/29488, a color photosensor array is described having a pixel sensor with three photodiode junctions stacked vertically, one on top of each other, with one deep junction, of depth about 2 microns, sensing red light, another intermediate-depth junction, of depth about 0.6 microns, sensing green light, and another shallow junction, of depth about 0.2 microns, sensing blue light.